U.S. Pat. Nos. 4,027,660 issued Jun. 7, 1977; and 4,082,085 issued Apr. 4, 1978 relate to a technique for performing differential leukocyte counts in a sample of anticoagulated whole blood which has been drawn into a capillary tube and centrifuged. A generally cylindrical float is disposed in the capillary tube in the blood sample during centrifugation. The float settles into the erythrocyte layer and extends through the buffy coat so as to physically elongate the leukocyte and platelet layers. A stain such as acridine orange is used to differentially color the different constituents which make up the buffy coat so that the buffy coat appears as a plurality of differently colored bands in the capillary tube (typically a glass capillary tube which is also called a Quantitative Buffy Coat or QBC tube). The layering of the constituents according to density during centrifugation allows cell counts to be made by measuring the distance between the boundaries of each cell band.
It is highly desirable to transfer a fluid (such as blood) into and fill a glass capillary tube such as that utilized in the above technique without opening a blood collection tube. It is desirable to limit the exposure of, for example, health care workers of any kind, to possible blood-borne pathogens to whatever extent is technologically possible. The use of cap-piercers with impedance style hematology analyzers has now become commonplace.
One device which is presently available and addresses these concerns is called Diff-Safe.TM. Blood Dispenser (Patent Pending). This device is manufactured for Alpha Scientific Corporation, P.O. Box 617, Wayne, Penn. 19807-0617. The purpose of the device is to allow a drop of blood from an EDTA tube to be placed on a slide to prepare a differential smear without opening the blood tube. The device is a simple molded plastic part with a blunt cannula which pierces the EDTA blood tube closure. When the user presses the device against the slide a positive pressure is exerted inside the blood tube by a slight displacement of the elastomeric closure. This positive pressure forces a drop of blood out the cannula which is deposited on the slide
The present invention describes an improvement over this device which allows safe and effective transfer of a fluid such as blood from a blood collection tube into a glass capillary tube, without any spillage or danger of exposure. Such filling of a glass capillary tube can enable one to utilize these filled glass capillary tubes in, for example, the above-described QBC technique.